With the development of mobile internet technology, more and more multimedia content providers publish and sell multimedia information over a network. Because of the uncontrollability of the internet and characteristics of digital media, such as the lossless copy and transmission, the copyright protection of digital multimedia information becomes very difficult.
With respect to this problem, a conventional solution is generally to limit different users to enjoy and download different multimedia files by setting user rights. For example, a multimedia content provider only permits a paid user to enjoy and download specific copyrighted multimedia files. However, the user with permission may issue the downloaded high-quality multimedia files onto the network, and other users can also enjoy the high-quality multimedia files even without the permission. Obviously, although the conventional technology has limited piracy to some extent, there is still a need for improved techniques to further protect the copyright of digital multimedia information.